During reactive extrusion, low molecular weight, low viscosity ethylene-based polymers have lower melt temperatures, due to less viscous energy dissipation, as compared to higher molecular weight, higher viscosity polymers. As a consequence, long extruders are required to raise melt temperatures to induce peroxide initiated grafting.
Grafting low molecular weight ethylene-based polymers currently requires high extruder length to diameter (L/D) ratios (>60 L/D, and preferably >80 L/D). This can be achieved using two tandem extruders (for example, 40 L/D each). At low melt temperatures, typical peroxides have half lives that are too long for a standard reactive extrusion process. Thus, a significant portion of the length of the extruder is needed to heat the low viscosity polymer to a temperature where the peroxide can decompose, and induce radicals for appreciable grafting onto the polymer. However, a problem arises in the pelletization of these grafted polymers. At the temperature where grafting occurs (>200° C. for typical peroxides), the low viscosity grafted polymers have very low melt strength, and cannot be pelletized underwater. As a result, a significant length of the extruder is required to cool the grafted-polymer melt to low enough temperatures for pelletization. Grafted polymers and/or extrusion processes are described in the following references: WO 2007/146875 and WO 2006/039774. However, there remains a need for new grafting processes for low molecular weight ethylene-based polymers. These needs have been met by the following invention.